However, in a recent discussion with a non-Christian, where I was using presuppositional apologetics, I was accused of using circular reasoning to argue my case. He claims that it is invalid to assume God exists to argue that God exists. On the surface, this seems to make sense. But I still firmly believe that it’s valid to presuppose that God exists.

How should I respond to his claims that my arguments are invalid due to circular reasoning?

We agree that presuppositional apologetics is the ultimate biblical approach to apologetics. The common accusation that the presuppositionalist uses circular reasoning is actually true. In fact, everyone uses some degree of circular reasoning when defending his ultimate standard (though not everyone realizes this fact). Yet if used properly, this use of circular reasoning is not arbitrary and, therefore, not fallacious.

Contrary to what your non-Christian friend said, circular reasoning is surprisingly a valid argument. The conclusion does follow from the premises. Circular reasoning is a logical fallacy only when it is arbitrary, proving nothing beyond what it assumes.

However, not all circular reasoning is fallacious. Certain standards must be assumed. Dr. Jason Lisle gave this example of a non-arbitrary use of circular reasoning:

While this argument is circular, it is a non-fallacious use of circular reasoning. Since we couldn’t prove anything apart from the laws of logic, we must presuppose the laws of logic even to prove they exist. In fact, if someone were trying to disprove that laws of logic exist, he’d have to use the laws of logic in his attempt, thereby refuting himself. Your non-Christian friend must agree there are certain standards that can be proven with circular reasoning.

Your basic presupposition—God exists and has revealed Himself in His inerrant, authoritative Word—is the ultimate standard. Presupposing God exists to argue that God exists is a reasonable circular argument because without the God of the Bible, we have no basis for assuming the laws of logic and their properties, let alone absolute morality or the uniformity of nature.

Your basic presupposition—God exists and has revealed Himself in His inerrant, authoritative Word—is the ultimate standard.

We’ve already established how the laws of logic must exist or else we wouldn’t have reason to debate. But a natural universe consisting of strictly matter in motion would not contain abstract laws of logic, and proving anything would be impossible.2 These laws do obviously exist because the biblical God exists, and the laws of logic stem from His nature—He is unchanging, universal, and immaterial.3

Also, absolute moral standards are dependent on the holy, sinless God of the Bible. He promises to judge those who violate His laws—each of us—by casting sinful unbelievers into the lake of fire or freeing sinful believers by His own Son’s blood on the Cross (2 Thessalonians 1:8–9; Ephesians 1:7). If the evolutionary worldview were true, we would be advanced animals acting on chemical impulses. Absolute moral standards would not exist.

Science itself requires the biblical God. Without the uniformity of nature, which can only be explained by God consistently upholding the universe, science would be a guessing game. In a random chance universe, we’d have no reason to expect the constancy of physical laws God has ordained, such as the law of gravity.

The links within this article give more detailed information about how to show your non-Christian friend that in order to make an argument, practice science, or expect absolute morality, he has to assume the biblical God exists. Basically, you are proving your presupposition by demonstrating the impossibility of God not existing. No wonder Scripture calls a person a fool who says, “There is no God” (Psalm 14:1). Knowledge and wisdom depend on the existence of the biblical God (Proverbs 1:7; Colossians 2:3).

As you humbly share, recognize this is an issue of the heart. We all inherently know the Creator, but many suppress that truth in unrighteousness, and their thinking becomes futile (Romans 1:18–22). Warn of the justice of God in punishing sin (Romans 6:23). Then share the grace of God in sending His Son to take that punishment for those who turn to the Lord Jesus in repentance and faith.